An exemplary conventional piston assembly for an internal combustion engine is generally indicated by reference numeral 1 in FIGS. 1 and 5. As illustrated in FIG. 5, the conventional piston assembly 1 includes a cylinder 2 having a cylinder interior 3. A piston head 6 having a combustion surface 7 is disposed in the cylinder interior 3 for reciprocation therein during a combustion cycle. A combustion chamber 4 is defined in the cylinder interior 3 between the walls of the cylinder 2 and the combustion surface 7 of the piston head 6. An elongated connecting rod 12 has a piston connecting end 16 which is pivotally attached to the piston head 6 via a wrist pin 15 and a crankshaft connecting end 13 which is opposite the piston connecting end 16. A crankshaft 18 includes a crankshaft body 19 and a crankshaft lobe 20 extending from the crankshaft body 19. The crankshaft lobe 20 of the crankshaft 18 is rotatably attached to the crankshaft connecting end 13 of the connecting rod 12 via a connecting pin 14. Reciprocation of the piston head 6 in the cylinder interior 3 of the cylinder 2 throughout the combustion cycle causes the connecting rod 12 to rotate the crankshaft 18 about a crankshaft axis of rotation 22.
The point of attachment between the piston head 6 and the connecting rod 12 at the wrist pin 15 is on the side of the crankshaft axis of rotation 22 which is proximate or nearer to the combustion surface 7 of the piston head 6. Consequently, as the reciprocating piston head 6 travels from the top-dead-center (TDC) position (the left-hand diagram in FIG. 5) to 90 degrees after TDC (the middle diagram in FIG. 5) in the cylinder interior 3 during the first half of the power stroke, the connecting pin 14 traverses the top or proximal arc of rotation, or the arc of rotation which is nearer or proximal to the combustion surface 7. Conversely, as the piston head 6 travels from 90 degrees after TDC (the middle diagram in FIG. 5) to the bottom-dead-center (BDC) position (the right-hand diagram in FIG. 5) during the second half of the power stroke, the connecting pin 14 traverses the bottom or distal arc of rotation, or the arc of rotation which is further from or distal to the combustion surface 7 of the piston head 6. As a result, the distance of travel of the piston head 6 from the TDC position to 90 degrees after TDC in the cylinder interior 3 is greater than the distance of travel of the piston head 6 from 90 degrees after TDC to the BDC position. This longer distance of travel of the piston head 6 during the first half relative to the second half of the power stroke results in incomplete combustion of fuel in the cylinder interior 3 throughout the combustion cycle.
Accordingly, a piston assembly is needed in which the distance of travel of the piston head from the TDC position to 90 degrees after TDC (the first half of the power stroke) is less than the distance of travel of the piston head from 90 degrees after TDC to the BDC position (the second half of the power stroke) to increase combustion time and provide a more constant volume for substantially complete fuel consumption during the initial part of the power stroke in an internal combustion engine.